Such processes are known in the art from for example WO-A-9505354, EP-A-0495547 and WO-A-01/87899. Although good activities towards a hydroformylation product are obtained, there is still room for improvement, especially when larger ethylenically unsaturated compounds are hydroformylated. It is furthermore desirable to provide such a hydroformylation process where high activities towards a hydroformylation product can be obtained when the process is carried out under acidic conditions.
WO-A-01/87899 relates amongst others to the carbonylation of ethylenically unsaturated compounds. It describes a specific class of bidentate diphosphines. The phosphorus atoms in these diphosphines are connected by a bridging group. A wide range of bridging groups is described. Cyclopentene is mentioned in passing as a possible bridging group. However, no bidentate diphosphines comprising a cyclopentene bridge are mentioned. Furthermore it is not indicated how such a cyclopentene bridge should be connected to the phosphorus atoms.
WO-A-0226690 relates to a process for the carbonylation of conjugated dienes. The examples describe the reaction of 1,3-butadiene and methanol to methylpentenoate in the presence of a catalyst comprising palladium acetate, a bidentate diphosphine and a carboxylic acid. Several bidentate diphosphines are exemplified. The examples show that, for the exemplified reaction with methanol, a catalyst system comprising 1,2-P,P′bis(9-phosphabicyclononyl) benzene as a bidentate diphosphine has only a moderate activity (400 mol/mol/hr), much lower than a catalyst system comprising R,S-meso-2,3-P,P′bis(9-phosphabicyclononyl)butane as a bidentate diphosphine (560 mol/mol/hr).